Method for transmitting a sounding reference signal in a wireless communication system, and apparatus for same

ABSTRACT

A method for transmitting a sounding reference signal (SRS) at a user equipment in a time division duplex (TDD) communication system; and the user equipment are discussed. The method includes receiving downlink control information (DCI) including a request of the SRS transmission. The DCI includes information for receiving downlink data using multiple antennas by the user equipment. The method further includes transmitting the SRS to the base station according to the request of the SRS transmission.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent application Ser. No. 14/567,909 filed on Dec. 11, 2014, which is a continuation of U.S. patent application Ser. No. 13/497,293 filed Jul. 23, 2012 (now U.S. Pat. No. 8,948,088, issued on Feb. 3, 2015), which is the national phase of PCT International Application No. PCT/KR2010/006475 filed Sep. 20, 2010, which claims the benefit of U.S. Provisional Application Nos. 61/244,424 filed on Sep. 21, 2009, 61/310,712 filed Mar. 5, 2010, and 61/316,820 filed on Mar. 23, 2010. The entire contents of all of the above applications are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication system, and more particularly, to a method and apparatus for transmitting an aperiodic sounding reference signal from a user equipment to a base station in a wireless communication system.

2. Discussion of the Related Art

As an example of a mobile communication system to which the present invention is applicable, a 3^(rd) Generation Partnership Project (3GPP) Long Term Evolution (LTE) communication system will be schematically described.

FIG. 1 is a diagram showing a network structure of an Evolved Universal Mobile Telecommunications System (E-UMTS) as a mobile communication system. The E-UMTS is an evolved form of the UMTS and has been standardized in the 3GPP. Generally, the E-UMTS may be called a Long Term Evolution (LTE) system. For details of the technical specifications of the UMTS and E-UMTS, refer to Release 7 and Release 8 of “3^(rd) Generation Partnership Project; Technical Specification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS mainly includes a User Equipment (UE) 120, base stations (or eNBs or eNode Bs) 110 a and 110 b, and an Access Gateway (AG) which is located at an end of a network (E-UTRAN) and which is connected to an external network. Generally, an eNB can simultaneously transmit multiple data streams for a broadcast service, a multicast service and/or a unicast service.

One or more cells may exist per eNB. The cell is set to use a bandwidth such as 1.25, 2.5, 5, 10, 15 or 20 MHz to provide a downlink or uplink transmission service to several UEs. Different cells may be set to provide different bandwidths. The eNB controls data transmission or reception of a plurality of UEs. The eNB transmits downlink (DL) scheduling information of DL data so as to inform a corresponding UE of time/frequency domain in which data is transmitted, coding, data size, and Hybrid Automatic Repeat and reQest (HARQ)-related information. In addition, the eNB transmits uplink (UL) scheduling information of UL data to a corresponding UE so as to inform the UE of a time/frequency domain, which may be used by the UE, coding, data size and HARQ-related information. An interface for transmitting user traffic or control traffic can be used between eNBs. A Core Network (CN) may include the AG and a network node or the like for user registration of the UE. The AG manages mobility of a UE on a Tracking Area (TA) basis. One TA includes a plurality of cells.

Although wireless communication technology has been developed up to Long Term Evolution (LTE) based on Wideband Code Division Multiple Access (WCDMA), the demands and the expectations of users and providers continue to increase. In addition, since other radio access technologies have been continuously developed, new technology evolution is required to secure high competitiveness in the future. Decrease in cost per bit, increase in service availability, flexible use of a frequency band, simple structure, open interface, suitable User Equipment (UE) power consumption and the like are required.

Recently, the standardization of the subsequent technology of the LTE is ongoing in the 3GPP. In the present specification, the above-described technology is called “LTE-Advanced” or “LTE-A”. The LTE system and the LTE-A system are different from each other in terms of system bandwidth. The LTE-A system aims to support a wide bandwidth of a maximum of 100 MHz. The LTE-A system uses carrier aggregation or bandwidth aggregation technology which achieves the wide bandwidth using a plurality of frequency blocks. The carrier aggregation enables the plurality of frequency blocks to be used as one large logical frequency band in order to use a wider frequency band. The bandwidth of each of the frequency blocks may be defined based on the bandwidth of a system block used in the LTE system. Each frequency block is transmitted using a component carrier.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method and apparatus for transmitting an aperiodic sounding reference signal from a user equipment to a base station in a wireless communication system.

The technical problems solved by the present invention are not limited to the above technical problems and those skilled in the art may understand other technical problems from the following description.

The object of the present invention can be achieved by providing a method for transmitting an aperiodic sounding reference signal (SRS) at a user equipment in a wireless communication system including receiving downlink control information from a base station, decoding a downlink control information (DCI) format for downlink transmission included in the downlink control information, checking an instruction to transmit the aperiodic SRS in the DCI format for downlink transmission, and transmitting the aperiodic SRS to the base station according to the instruction. If the downlink control channel is received via an n^(th) subframe, the aperiodic SRS may be transmitted via an (n+k)^(th) subframe (k≧4).

The method may further include receiving a transmission parameter of the aperiodic SRS through a higher layer. The DCI format for downlink transmission may include a transmission parameter of the aperiodic SRS. The DCI format for downlink transmission may be a DCI format for a multiple input multiple output (MIMO) system.

In another aspect of the present invention, there is provided a user equipment in a wireless communication system including a reception module configured to receive downlink control information from a base station, a processor configured to decode a downlink control information (DCI) format for downlink transmission included in the downlink control information and check an instruction to transmit the aperiodic SRS in the DCI format for downlink transmission, and a transmission module configured to transmit an aperiodic SRS to the base station according to the instruction. If the downlink control channel is received via an n^(th) subframe, the aperiodic SRS may be transmitted via an (n+k)^(th) subframe (k≧4).

The reception module may receive a transmission parameter of the aperiodic SRS through a higher layer. The DCI format for downlink transmission may include a transmission parameter of the aperiodic SRS. The DCI format for downlink transmission may be a DCI format for a multiple input multiple output (MIMO) system.

According to the embodiments of the present invention, it is possible to efficiently transmit an aperiodic sounding reference signal from a user equipment to a base station in a wireless communication system.

The effects of the present invention are not limited to the above-described effects and other effects which are not described herein will become apparent to those skilled in the art from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a network structure of an Evolved Universal Mobile Telecommunications System (E-UMTS) as an example of a mobile communication system.

FIG. 2 is a diagram showing a control plane and a user plane of a radio interface protocol architecture between a User Equipment (UE) and an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) based on a 3^(rd) Generation Partnership Project (3GPP) radio access network standard.

FIG. 3 is a diagram showing physical channels used in a 3GPP system and a general signal transmission method using the same.

FIG. 4 is a diagram showing the structure of a radio frame used in a Long Term Evolution (LTE) system.

FIG. 5 is a diagram showing the structure of an uplink subframe in an LTE system.

FIG. 6 is a block diagram showing a transmitter or receiver according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The configuration, operation and other features of the present invention will be understood by the embodiments of the present invention described with reference to the accompanying drawings. The following embodiments are examples of applying the technical features of the present invention to a 3^(rd) Generation Partnership Project (3GPP) system.

Hereinafter, a system in which a system band uses a single frequency block is referred to as a legacy system or a narrowband system. A system in which a system band includes a plurality of frequency blocks and at least one frequency blocks are used as a system block of a legacy system is referred to as an evolved system or a wideband system. The frequency block used as the legacy system block has the same size as the system block of the legacy system. The sizes of the remaining frequency blocks are not specially limited. However, in order to simplify a system, the size of the remaining frequency blocks may be determined based on the size of the system block of the legacy system. For example, a 3GPP LTE system and a 3GPP LTE-A system are evolved from a legacy system.

Based on the above definition, in the present specification, a 3GPP LTE system is called an LTE system or a legacy system. A user equipment (UE) which supports an LTE system is called an LTE UE or a legacy UE. A 3GPP LTE-A system is called an LTE-A system or an evolved system. A UE which supports an LTE-A system is called an LTE-A UE or an evolved UE.

Although, for convenience, the embodiments of the present invention are described using the LTE system and the LTE-A system in the present specification, the embodiments of the present invention are applicable to any communication system corresponding to the above definition. In addition, although the embodiments of the present invention are described based on a Frequency Division Duplex (FDD) scheme in the present specification, the embodiments of the present invention may be easily modified and applied to a Half-Duplex FDD (H-FDD) scheme or a Time Division Duplex (TDD) scheme.

FIG. 2 shows a control plane and a user plane of a radio interface protocol between a UE and an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) based on a 3GPP radio access network standard. The control plane refers to a path used for transmitting control messages used for managing a call between the UE and the network. The user plane refers to a path used for transmitting data generated in an application layer, e.g., voice data or Internet packet data.

A physical (PHY) layer of a first layer provides an information transfer service to a higher layer using a physical channel. The PHY layer is connected to a Medium Access Control (MAC) layer located on a higher layer via a transport channel. Data is transported between the MAC layer and the PHY layer via the transport channel. Data is also transported between a physical layer of a transmitting side and a physical layer of a receiving side via a physical channel. The physical channel uses a time and a frequency as radio resources. More specifically, the physical channel is modulated using an Orthogonal Frequency Division Multiple Access (OFDMA) scheme in downlink and is modulated using a Single-Carrier Frequency Division Multiple Access (SC-FDMA) scheme in uplink.

A Medium Access Control (MAC) layer of a second layer provides a service to a Radio Link Control (RLC) layer of a higher layer via a logical channel. The RLC layer of the second layer supports reliable data transmission. The function of the RLC layer may be implemented by a functional block within the MAC. A Packet Data Convergence Protocol (PDCP) layer of the second layer performs a header compression function to reduce unnecessary control information for efficient transmission of an Internet Protocol (IP) packet such as an lPv4 packet or an IPv6 packet in a radio interface having a relatively small bandwidth.

A Radio Resource Control (RRC) layer located at the bottom of a third layer is defined only in the control plane and is responsible for control of logical, transport, and physical channels in association with configuration, re-configuration, and release of Radio Bearers (RBs). The RB is a service that the second layer provides for data communication between the UE and the network. To accomplish this, the RRC layer of the UE and the RRC layer of the network exchange RRC messages. The UE is in an RRC connected mode if an RRC connection has been established between the RRC layer of the radio network and the RRC layer of the UE. Otherwise, the UE is in an RRC idle mode. A Non-Access Stratum (NAS) layer located above the RRC layer performs functions such as session management and mobility management.

One cell of the eNB is set to use a bandwidth such as 1.25, 2.5, 5, 10, 15 or 20 MHz to provide a downlink or uplink transmission service to several UEs. Different cells may be set to provide different bandwidths.

Downlink transport channels for transmission of data from the network to the UE include a Broadcast Channel (BCH) for transmission of system information, a Paging Channel (PCH) for transmission of paging messages, and a downlink Shared Channel (SCH) for transmission of user traffic or control messages. Traffic or control messages of a downlink multicast or broadcast service may be transmitted through a downlink SCH and may also be transmitted through a downlink multicast channel (MCH). Uplink transport channels for transmission of data from the UE to the network include a Random Access Channel (RACH) for transmission of initial control messages and an uplink SCH for transmission of user traffic or control messages. Logical channels, which are located above the transport channels and are mapped to the transport channels, include a Broadcast Control Channel (BCCH), a Paging Control Channel (PCCH), a Common Control Channel (CCCH), a Multicast Control Channel (MCCH) and a Multicast Traffic Channel (MTCH).

FIG. 3 is a diagram showing physical channels used in a 3GPP system and a general signal transmission method using the same.

A UE performs an initial cell search operation such as synchronization with an eNB when power is turned on or the UE enters a new cell (S301). The UE may receive a Primary Synchronization Channel (P-SCH) and a Secondary Synchronization Channel (S-SCH) from the eNB, perform synchronization with the eNB, and acquire information such as a cell ID. Thereafter, the UE may receive a physical broadcast channel from the eNB so as to acquire broadcast information within the cell. Meanwhile, the UE may receive a Downlink Reference Signal (DL RS) so as to confirm a downlink channel state in the initial cell search step.

The UE which completes the initial cell search may receive a Physical Downlink Control Channel (PDCCH) and a Physical Downlink Shared Channel (PDSCH) according to information included in the PDCCH so as to acquire more detailed system information (S302).

Meanwhile, if the eNB is initially accessed or radio resources for signal transmission are not present, the UE may perform a Random Access Procedure (RACH) (step S303 to S306) with respect to the eNB. In this case, the UE may transmit a specific sequence through a Physical Random Access Channel (PRACH) as a preamble (S303 and S305), and receive a response message of the preamble through the PDCCH and the PDSCH corresponding thereto (S304 and S306). In the case of contention-based RACH, a contention resolution procedure may be further performed.

The UE which performs the above procedures may perform PDCCH/PDSCH reception (S307) and Physical Uplink Shared Channel PUSCH)/Physical Uplink Control Channel (PUCCH) transmission (S308) as a general uplink/downlink signal transmission procedure. The control information transmitted from the UE to the eNB in uplink or transmitted from the eNB to the UE in downlink includes a downlink/uplink ACK/NACK signal, a Channel Quality Indicator (CQI), a Precoding Matrix Index (PMI), a Rank Indicator (RI), and the like. In the case of the 3GPP LTE system, the UE may transmit the control information such as CQI/PMI/RI through the PUSCH and or the PUCCH.

FIG. 4 is a diagram showing the structure of a radio frame used in a Long Term Evolution (LTE) system.

Referring to FIG. 4, the radio frame has a length of 10 ms (327200·T_(s)) and includes 10 subframes with the same size. Each of the subframes has a length of 1 ms and includes two slots. Each of the slots has a length of 0.5 ms (15360·T_(s)), T_(s) denotes a sampling time, and is represented by T_(s)=1/(15 kHz×2048)=3.2552×10⁻⁸ (about 33 ns). Each slot includes a plurality of OFDM or SC-FDMA symbols in a time domain, and includes a plurality of resource blocks (RBs) in a frequency domain. In the LTE system, one RB includes 12 subcarriers×7(6) OFDM or SC-FDMA symbols. A Transmission Time Interval (TTI) which is a unit time for transmission of data may be determined in units of one or more subframes. The structure of the radio frame is only exemplary and the number of subframes included in the radio frame, the number of slots included in the subframe, or the number of OFDM or SC-FDMA symbols included in the slot may be variously changed.

FIG. 5 is a diagram showing the structure of an uplink subframe in an LTE system.

Referring to FIG. 5, a subframe 500 having a length of 1 ms, which is a basic unit of LTE uplink transmission, includes two slots 501 each having a length of 0.5 ms. In case of normal cyclic prefix (CP), each slot includes seven symbols 502 and one symbol corresponds to one SC-FDMA symbol. An RB 503 is a resource allocation unit corresponding to 12 subcarriers in a frequency domain and one slot in a time domain. The structure of the uplink subframe of the LTE is roughly divided into a data region 504 and a control region 505. The data region refers to a series of communication resources used to transmit data such as voice or packets to each UE and corresponds to resources excluding resources belonging to the control region in a subframe. The control region refers to a series of communication resources used to transmit a downlink channel quality report from each UE, reception ACK/NACK for a downlink signal, an uplink scheduling request, etc.

As shown in FIG. 5, a region 506 for transmitting a sounding reference signal (SRS) within one subframe is a part including SC-FDMA symbols located at the last of a time axis in one subframe and the SRS is transmitted via a data transmission band on a frequency axis. SRSs of several UEs transmitted using the last SC-FDMA symbols of the same subframe may be distinguished according to frequency positions.

The SRS is composed of constant amplitude zero auto correlation (CAZAC) sequences. SRSs transmitted from several UEs are CAZAC sequences r^(SRS)(n)=r_(u,v) ^((α))(n) having different cyclic shift values a according to Equation 1.

$\begin{matrix} {\alpha = {2\pi \frac{n_{SRS}^{cs}}{8}}} & {{Equation}\mspace{14mu} 1} \end{matrix}$

where, n_(SRS) ^(cs) is a value set to each UE by a higher layer and has an integer value of 0 to 7. Accordingly, the cyclic shift value may have eight values according to n_(SRS) ^(cs).

CAZAC sequences generated from one CAZAC sequence through cyclic shift have zero correlation values with sequences having different cyclic shift values. Using such property, SRSs of the same frequency domain may be divided according to CAZAC sequence cyclic shift values. The SRS of each UE is allocated to the frequency according to a parameter set by the eNB. The UE performs frequency hopping of the SRS so as to transmit the SRS with an overall uplink data transmission bandwidth.

Hereinafter, a detailed method of mapping physical resources for transmitting SRSs in an LTE system will be described.

In order to satisfy transmit power P_(SRS) of a UE, an SRS sequence r^(SRS)(n) is first multiplied by an amplitude scaling factor β_(SRS) and is then mapped to a resource element (RE) having an index (k, l) from r^(SRS)(0) by Equation 2.

$\begin{matrix} {a_{{{2k} + k_{0}},I} = \left\{ \begin{matrix} {\beta_{SRS}{r^{SRS}(k)}} & {{k = 0},1,\ldots \mspace{14mu},{M_{{sc},b}^{RS} - 1}} \\ 0 & {otherwise} \end{matrix} \right.} & {{Equation}\mspace{14mu} 2} \end{matrix}$

where, k₀ denotes a frequency domain start point of an SRS and is defined by Equation 3.

$\begin{matrix} {k_{0} = {k_{0}^{\prime} + {\sum\limits_{b = 0}^{B_{SRS}}{2M_{{sc},b}^{RS}n_{b}}}}} & {{Equation}\mspace{14mu} 3} \end{matrix}$

where, n_(b) denotes a frequency position index. k′⁰ for a general uplink subframe is defined by Equation 4 and k′₀ for an uplink pilot time UpPTS is defined by Equation 5.

$\begin{matrix} {k_{0}^{\prime} = {{\left( {\left\lfloor {N_{RB}^{UL}/2} \right\rfloor - {m_{{SRS},0}/2}} \right)N_{SC}^{RB}} + k_{TC}}} & {{Equation}\mspace{14mu} 4} \\ {k_{0}^{\prime} = \left\{ \begin{matrix} {{\left( {N_{RB}^{UL} - m_{{SRS},0}^{\max}} \right)N_{sc}^{RB}} + k_{TC}} & {{{{if}\left( {{\left( {n_{f}\mspace{11mu} {mod}\mspace{11mu} 2} \right) \times \left( {2 - N_{SP}} \right)} + n_{bf}} \right)}{mod}\mspace{14mu} 2} = 0} \\ k_{TC} & {otherwise} \end{matrix} \right.} & {{Equation}\mspace{14mu} 5} \end{matrix}$

In Equations 4 and 5, k_(TC) denotes a transmissionComb parameter signaled to a UE via a higher layer and has a value of 0 or 1. In addition, n_(hf) is 0 in an uplink pilot time slot of a first half frame and is 0 in an uplink pilot slot of a second half frame. M_(sc,b) ^(RS) is the length, that is, the bandwidth, if the SRS sequence expressed in subcarrier units defined by Equation 6.

M _(sc,b) ^(RS) =m _(SRS,b) N _(sc) ^(RB)/2   Equation 6

In Equation 6, m_(SRS,b) is a value signaled from an eNB according to an uplink bandwidth N_(RB) ^(UL) as shown in Tables 1 to 4.

In order to acquire m_(SRS,b), a cell-specific parameter C_(SRS) having an integer value of 0 to 7 and a UE-specific parameter B_(SRS) having an integer value of 0 to 3 are necessary. The values of C_(SRS) and B_(SRS) are provided by a higher layer.

TABLE 1 b_(hop) = 0, 1, 2, 3 and 6 ≦ N_(RB) ^(UL) ≦ 40 SRS SRS- SRS- SRS- SRS- bandwidth Bandwidth Bandwidth Bandwidth Bandwidth configuration B_(SRS) = 0 B_(SRS) = 1 B_(SRS) = 2 B_(SRS) = 3 C_(SRS) m_(SRS, b) N_(b) m_(SRS, b) N_(b) m_(SRS, b) N_(b) m_(SRS, b) N_(b) 0 36 1 12 3 4 3 4 1 1 32 1 16 2 8 2 4 2 2 24 1 4 6 4 1 4 1 3 20 1 4 5 4 1 4 1 4 16 1 4 4 4 1 4 1 5 12 1 4 3 4 1 4 1 6 8 1 4 2 4 1 4 1 7 4 1 4 1 4 1 4 1

TABLE 2 b_(hop) = 0, 1, 2, 3 and 40 < N_(RB) ^(UL) ≦ 60 SRS SRS- SRS- SRS- SRS- bandwidth Bandwidth Bandwidth Bandwidth Bandwidth configuration B_(SRS) = 0 B_(SRS) = 1 B_(SRS) = 2 B_(SRS) = 3 C_(SRS) m_(SRS, 0) N₀ m_(SRS, 1) N₁ m_(SRS, 2) N₂ m_(SRS, 3) N₃ 0 48 1 24 2 12 2 4 3 1 48 1 16 3 8 2 4 2 2 40 1 20 2 4 5 4 1 3 36 1 12 3 4 3 4 1 4 32 1 16 2 8 2 4 2 5 24 1 4 6 4 1 4 1 6 20 1 4 5 4 1 4 1 7 16 1 4 4 4 1 4 1

TABLE 3 b_(hop) = 0, 1, 2, 3 and 60 < N_(RB) ^(UL) ≦ 80 SRS SRS- SRS- SRS- SRS- bandwidth Bandwidth Bandwidth Bandwidth Bandwidth configuration B_(SRS) = 0 B_(SRS) = 1 B_(SRS) = 2 B_(SRS) = 3 C_(SRS) m_(SRS, 0) N₀ m_(SRS, 1) N₁ m_(SRS, 2) N₂ m_(SRS, 3) N₃ 0 72 1 24 3 12 2 4 3 1 64 1 32 2 16 2 4 4 2 60 1 20 3 4 5 4 1 3 48 1 24 2 12 2 4 3 4 48 1 16 3 8 2 4 2 5 40 1 20 2 4 5 4 1 6 36 1 12 3 4 3 4 1 7 32 1 16 2 8 2 4 2

TABLE 4 b_(hop) = 0, 1, 2, 3 and 80 < N_(RB) ^(UL) ≦ 110 SRS SRS- SRS- SRS- SRS- bandwidth Bandwidth Bandwidth Bandwidth Bandwidth configuration B_(SRS) = 0 B_(SRS) = 1 B_(SRS) = 2 B_(SRS) = 3 C_(SRS) m_(SRS, 0) N₀ m_(SRS, 1) N₁ m_(SRS, 2) N₂ m_(SRS, 3) N₃ 0 96 1 48 2 24 2 4 6 1 96 1 32 3 16 2 4 4 2 80 1 40 2 20 2 4 5 3 72 1 24 3 12 2 4 3 4 64 1 32 2 16 2 4 4 5 60 1 20 3 4 5 4 1 6 48 1 24 2 12 2 4 3 7 48 1 16 3 8 2 4 2

As described above, the UE may perform frequency hopping of the SRS so as to transmit the SRS with the overall uplink data transmission bandwidth. Such frequency hopping is set by a parameter b_(hop) having a value of 0 to 3 received from a higher layer.

If frequency hopping of the SRS is deactivated, that is, if b_(hop)≧B_(SRS), a frequency position index n_(b) has a constant value as shown in Equation 7. Here, n_(RRC) is a parameter received from a higher layer.

n _(b)=└4n _(RRC) /m _(SRS,b)┘mod N _(b)   Equation 7

Meanwhile, if frequency hopping of the SRS is activated, that is, b_(hop)<B_(SRS), a frequency position index n_(b) is defined by Equations 8 and 9.

$\begin{matrix} {n_{b} = \left\{ \begin{matrix} {\left\lfloor {4{n_{RRC}/m_{{SRS},b}}} \right\rfloor {mod}\mspace{14mu} N_{b}} & {b \leq b_{hop}} \\ {\left\{ {{F_{b}\left( n_{SRS} \right)} + \left\lfloor {4{n_{RRC}/m_{{SRS},b}}} \right\rfloor} \right\} {mod}\mspace{14mu} N_{b}} & {otherwise} \end{matrix} \right.} & {{Equation}\mspace{14mu} 8} \\ {{F_{b}\left( n_{SRS} \right)} = \left\{ \begin{matrix} {{\left( {N_{b}/2} \right)\left\lfloor \frac{n_{SRS}{mod}\mspace{11mu} {\prod\limits_{b^{\prime} = b_{hop}}^{b}\; N_{b^{\prime}}}}{\prod\limits_{b^{\prime} = b_{hop}}^{b}\; N_{b^{\prime}}} \right\rfloor} + \left\lfloor \frac{n_{SRS}{mod}\mspace{11mu} {\prod\limits_{b^{\prime} = b_{hop}}^{b}\; N_{b^{\prime}}}}{2{\prod\limits_{b^{\prime} = b_{hop}}^{b - 1}\; N_{b^{\prime}}}} \right\rfloor} & {{if}\mspace{14mu} N_{b}\mspace{14mu} {even}} \\ {\left\lfloor {N_{b}/2} \right\rfloor \left\lfloor {n_{SRS}/{\prod\limits_{b^{\prime} = b_{hop}}^{b}\; N_{b^{\prime}}}} \right\rfloor} & {{if}\mspace{14mu} N_{b}\mspace{14mu} {odd}} \end{matrix} \right.} & {{Equation}\mspace{14mu} 9} \end{matrix}$

where, n_(SRS) is a parameter used to calculate the number of times of transmission of the SRS and is defined by Equation 10.

Equation 10

$\begin{matrix} {n_{SRS} = \left\{ \begin{matrix} {{{2N_{SP}n_{f}} + {2\left( {N_{SP} - 1} \right)\left\lfloor \frac{n_{s}}{10} \right\rfloor} + \left\lfloor \frac{T_{offset}}{T_{{offset}\; {\_ \max}}} \right\rfloor},} & {{for}\mspace{14mu} 2m\; s\mspace{14mu} {SRS}\mspace{14mu} {periodicity}\mspace{14mu} {of}\mspace{14mu} {TDD}\mspace{14mu} {frame}\mspace{14mu} {structure}} \\ {\left\lfloor {\left( {{n_{f} \times 10} + \left\lfloor {n_{s}/2} \right\rfloor} \right)/T_{SRS}} \right\rfloor,} & {otherwise} \end{matrix} \right.} & {\; {{Equation}\mspace{14mu} 10}} \end{matrix}$

In Equation 10, T_(SRS) denotes the periodicity of an SRS and T_(offset) denotes a subframe offset of an SRS. In addition, n_(s) denotes a slot number and n_(f) denotes a frame number.

A UE-specific SRS configuration index I_(SRS) for setting the periodicity T_(SRS) and the subframe offset T_(offset) of a UE-specific SRS signal is shown in Tables 5 and 6 according to FDD and TDD. In particular, Table 5 shows the SRS configuration index for FDD and Table 6 shows the SRS configuration index for TDD.

TABLE 5 SRS SRS SRS Configuration Periodicity Subframe Index I_(SRS) T_(SRS) (ms) Offset T_(offset) 0-1 2 I_(SRS) 2-6 5 I_(SRS)-2  7-16 10 I_(SRS)-7 17-36 20 I_(SRS)-17 37-76 40 I_(SRS)-37  77-156 80 I_(SRS)-77 157-316 160 I_(SRS)-157 317-635 320 I_(SRS)-317  637-1023 reserved reserved

TABLE 6 SRS SRS Configuration Periodicity Subframe Index I_(SRS) T_(SRS) (ms) Offset T_(offset) 0 2 0, 1 1 2 0, 2 2 2 1, 2 3 2 0, 3 4 2 1, 3 5 2 0, 4 6 2 1.4 7 2 2, 3 8 2 2, 4 9 2 3, 4 10-14 5 I_(SRS)-10 15-24 10 I_(SRS)-15 25-44 20 I_(SRS)-25 45-84 40 I_(SRS)-45  85-164 80 I_(SRS)-85 165-324 160 I_(SRS)-165 325-644 320 I_(SRS)-325  645-1023 reserved reserved

As described above, the UE receives parameters from the eNB through RRC signaling and transmits a periodic SRS. In contrast, the eNB instructs the UE to transmit an aperiodic SRS and the UE transmits the aperiodic SRS to the eNB according to the instruction.

Unlike the periodic SRS defined in the LTE system, if transmission of an aperiodic SRS is additionally instructed using L1/L2 control signaling, the additionally transmitted aperiodic SRS may be configured to be transmitted once or a restricted number of times or may be configured to be transmitted with predetermined periodicity. Control signaling which may be transmitted one time or a restricted number of times may be RRC signaling or L1 control signaling or may be predefined between the UE and the eNB so as to prevent additional overhead for additional signaling. Information about a subframe or subframe group via which an SRS is transmitted may also be included in L1/L2 control signaling.

In transmission of an aperiodic SRS, a symbol via which an additional SRS is transmitted may be configured to be allocated to the same subframe as a subframe to which the periodic SRS is allocated or a subframe different from the subframe to which the periodic SRS is allocated. A method of allocating the symbol to the subframe different from the subframe to which the periodic SRS is allocated refers to a method of setting a transmit interval of a symbol allocated to an aperiodic SRS to a subset of UE-specific SRS periodicity, that is, 2 ms, 4 ms, 5 ms, 10 ms or 20 ms which is a multiple of periodicity, when UE-specific SRS periodicity defined in the conventional LTE system is 1 ms.

More specifically, in the conventional LTE system, a subframe via which an SRS is periodically transmitted has a cell-specific configuration. As described above, if the symbol for the additionally transmitted aperiodic SRS is configured to be allocated to the same subframe as a cell-specific subframe to which the periodic SRS is allocated, the additionally transmitted SRS may have the same configuration as the cell-specific configuration or a subset of subframes which are configured to periodically transmit the SRS may be allocated for the additionally transmitted SRS.

That is, the additional SRS indicated by L1/L2 control signaling may be transmitted via a symbol reserved for transmitting the periodic SRS in a subframe via which the periodic SRS may be transmitted, another symbol reserved for transmitting the aperiodic SRS, or a symbol allocated or reserved for transmitting an uplink DM-RS.

The aperiodic SRS may be configured to be transmitted only via a predetermined cell-specific subframe configured to transmit the existing SRS and PUSCH puncturing is performed only in the predetermined cell-specific subframe so as to minimize uplink data throughput loss.

As parameters of the aperiodic SRS, resources used to transmit the periodic SRS, e.g., a cell-specific SRS bandwidth configuration, a UE-specific SRS bandwidth configuration, a frequency start position, a transmissionComb parameter, etc. may be used.

Alternatively, the parameters of the aperiodic SRS may be used as an RRC control signal similarly to a method used to transmit the periodic SRS, and an additional SRS may be transmitted using resources used to transmit the additional SRS, e.g., a cell-specific SRS bandwidth, a UE-specific SRS bandwidth, a frequency start position, a transmissionComb, etc.

Alternatively, the aperiodic SRS may be transmitted using an entire bandwidth usable in a system bandwidth, regardless of a cell-specific SRS bandwidth configuration and a UE-specific SRS bandwidth configuration. For example, an SRS occupying 24 RBs may be transmitted if a system bandwidth is 5 MHz, an SRS occupying 48 RBs may be transmitted if a system bandwidth is 10 MHz, an SRS occupying 72 RBs may be transmitted if a system bandwidth is 15 MHz, and an SRS occupying 96 RBs may be transmitted if a system bandwidth is 20 MHz.

Meanwhile, time resources used to transmit the aperiodic SRS, that is, a subframe position, follows a configuration included in downlink control information (DCI) or the aperiodic SRS may be transmitted via a subframe having a specific relationship. Hereinafter, a method of signaling transmission of an aperiodic SRS will be described.

First, a method of signaling an instruction to transmit an aperiodic SRS in a DCI format for uplink transmission may be considered. That is, if an eNB signals an instruction to transmit the aperiodic SRS via an n^(th) subframe in the DCI format for uplink transmission, a UE may decode the received uplink DCI format and transmit the aperiodic SRS to the eNB via an (n+k)^(th) subframe (k≧4).

However, in the case of a TDD system, an (n+k)^(th) subframe may not be an uplink subframe. If collision with a periodic SRS occurs, transmission of the aperiodic SRS may not be ensured.

Accordingly, a method of signaling an instruction to transmit the aperiodic SRS in a DCI format for downlink transmission is more preferable. In general, since the number of times of decoding the DCI format for downlink transmission at the UE is greater than the number of times of decoding of the DCI format for uplink transmission, the UE may efficiently cope with a sounding request of the base station.

First, if the eNB instructs only triggering/release or activation/deactivation signaling of the aperiodic SRS in a downlink DCI format, the amount of signaling information is not large, an unused information bit or bits in the DCI format for downlink transmission used in the LTE system or a combination of specific code points usable in the DCI format for downlink transmission may be used. In this case, the parameters of the SRS may be signaled through a higher layer, that is, an RRC layer, in advance. In addition, an aperiodic SRS does not satisfy backward compatibility for the LTE system, the aperiodic SRS may not be used in the LTE system, that is, Rel-8/9, but may be used in the LTE-A system, that is, subsequent Releases of Rel-10. A method of using a DCI format for downlink transmission newly defined in the LTE-A system may be used. For example, a method of using a DCI format for downlink transmission for an 8×8 MIMO system newly defined in Rel-10 may be considered.

In addition, even if all parameters for SRS transmission as well as triggering/release or activation/deactivation of the aperiodic SRS are dynamically signaled using DCI for downlink transmission, under the condition that a PDSCH is not transmitted in downlink, an unused information bit or bits in a DCI format for downlink transmission used in the LTE system or a combination of specific code points in the DCI format for downlink transmission may be used. In this case, all parameters for the UE-specific SRSs among the above-described SRSs or parameters of a subset of UE-specific parameters, e.g., cyclic shift (CS), transmissionComb and a UE-specific SRS bandwidth, may be dynamically signaled using a DCI format for downlink transmission and the remaining UE-specific parameters and the cell-specific parameters of the above-described SRSs may be signaled in advance through a higher layer, that is, an RRC layer. In this case, a method of using a DCI format for downlink transmission newly defined in the LTE-A system may be considered. For example, a method of using a DCI format for downlink transmission for an 8×8 MIMO system newly defined in Rel-10 may be considered. For example, the DCI format for downlink transmission newly defined in the LTE-A system, for example, a DCI format for downlink transmission for an 8×8 MIMO system may be used.

FIG. 6 is a block diagram showing a transmitter or receiver according to an embodiment of the present invention. The transmitter or receiver may be a part of an eNB or a UE.

Referring to FIG. 6, a transmitter/receiver 600 includes a processor 610, a memory 620, a Radio Frequency (RF) module 630, a display module 640 and a user interface module 650.

The transmitter/receiver 600 is shown for convenience of description and some modules thereof may be omitted. In addition, the transmitter/receiver 600 may further include necessary modules. In addition, some modules of the transmitter/receiver 600 may be subdivided. The processor 610 is configured to perform an operation of the embodiment of the present invention described with respect to the drawings.

More specifically, if the transmitter/receiver 600 is a part of an eNB, the processor 610 may perform a function for generating a control signal and mapping the control signal to a control channel set within a plurality of frequency blocks. If the transmitter/receiver 600 is a part of a UE, the processor 610 may confirm a control channel indicated thereto from a signal received through a plurality of frequency blocks and extract a control signal therefrom.

Thereafter, the processor 610 may perform a necessary operation based on the control signal. For a detailed description of the operation of the processor 610, reference may be made to the description associated with FIGS. 1 to 5.

The memory 620 is connected to the processor 610 so as to store an operating system, an application, program code, data and the like. The RF module 630 is connected to the processor 610 so as to perform a function for converting a baseband signal into a radio signal or converting a radio signal into a baseband signal. The RF module 630 performs analog conversion, amplification, filtering and frequency up-conversion or inverse processes thereof. The display module 640 is connected to the processor 610 so as to display a variety of information. As the display module 640, although not limited thereto, a well-known device such as a Liquid Crystal Display (LCD), a Light Emitting Diode (LED), or an Organic Light Emitting Diode (OLED) may be used. The user interface module 650 is connected to the processor 610 and may be configured by a combination of well-known user interfaces such as a keypad and a touch screen.

The above-described embodiments are proposed by combining constituent components and characteristics of the present invention according to a predetermined format. The individual constituent components or characteristics should be considered to be optional factors on the condition that there is no additional remark. If required, the individual constituent components or characteristics may not be combined with other components or characteristics. Also, some constituent components and/or characteristics may be combined to implement the embodiments of the present invention. The order of operations to be disclosed in the embodiments of the present invention may be changed to another. Some components or characteristics of any embodiment may also be included in other embodiments, or may be replaced with those of the other embodiments as necessary. Moreover, it will be apparent that some claims referring to specific claims may be combined with another claims referring to the other claims other than the specific claims to constitute the embodiment or add new claims by means of amendment after the application is filed.

The above-mentioned embodiments of the present invention are disclosed on the basis of a data communication relationship between a base station and a user equipment. Specific operations to be conducted by the base station in the present invention may also be conducted by an upper node of the base station as necessary. In other words, it will be obvious to those skilled in the art that various operations for enabling the base station to communicate with the user equipment in a network composed of several network nodes including the base station will be conducted by the base station or other network nodes other than the base station. The term “Base Station” may be replaced with the terms fixed station, Node-B, eNode-B (eNB), or access point as necessary. The term “terminal” may also be replaced with the term user equipment (UE), subscriber station (SS) or mobile subscriber station (MSS) as necessary.

The embodiments of the present invention can be implemented by a variety of means, for example, hardware, firmware, software, or a combination thereof In the case of implementing the present invention by hardware, the present invention can be implemented through application specific integrated circuits (ASICs), Digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), a processor, a controller, a microcontroller, a microprocessor, etc.

If operations or functions of the present invention are implemented by firmware or software, the present invention can be implemented in the form of a variety of formats, for example, modules, procedures, functions, etc. The software codes may be stored in a memory unit so as to be driven by a processor. The memory unit may be located inside or outside of the processor, so that it can communicate with the aforementioned processor via a variety of well-known parts.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

The present invention is applicable to a wireless communication system and, more particularly, to a method and apparatus for transmitting a sounding reference signal in a wireless communication system to which carrier aggregation is applied. 

What is claimed is:
 1. A method for transmitting a sounding reference signal (SRS) at a user equipment in a time division duplex (TDD) communication system, the method comprising: receiving downlink control information (DCI) including a request of the SRS transmission, wherein the DCI includes information for receiving downlink data using multiple antennas by the user equipment; and transmitting the SRS to the base station according to the request of the SRS transmission.
 2. The method according to claim 1, wherein the user equipment is configured with at least one parameter of the SRS by radio resource control (RRC) layer signaling.
 3. The method according to claim 1, wherein the DCI includes a request of the SRS release.
 4. The method according to claim 3, further comprising: stopping the SRS transmission according to the request of the SRS release.
 5. The method according to claim 1, wherein the DCI includes at least one parameter of the SRS.
 6. The method according to claim 1, wherein the SRS is transmitted on a subframe configured cell-specifically for the SRS.
 7. The method according to claim 1, wherein, if the downlink control information is received on a subframe #n, the SRS is transmitted on a subframe #(n+k)th (where k≧4).
 8. A user equipment in a time division duplex (TDD) communication system, the user equipment comprising: a reception module configured to receive downlink control information (DCI) including a request of a sounding reference signal (SRS) transmission, wherein the DCI includes information for receiving downlink data using multiple antennas by the user equipment; and a transmission module configured to transmit the SRS to the base station according to the request of the SRS transmission.
 9. The user equipment according to claim 8, wherein the user equipment is configured with at least one parameter of the SRS by radio resource control (RRC) layer signaling.
 10. The user equipment according to claim 8, wherein the DCI includes a request of the SRS release.
 11. The user equipment according to claim 10, wherein the reception module is further configured to stop the SRS transmission according to the request of the SRS release.
 12. The user equipment according to claim 8, wherein the DCI includes at least one parameter of the SRS.
 13. The user equipment according to claim 8, wherein the transmission module is configured to transmit the SRS on a subframe configured cell-specifically for the SRS.
 14. The user equipment according to claim 8, wherein, if the downlink control information is received on a subframe #n, the transmission module is configured to transmit the SRS on a subframe #(n+k)th, where k≧4. 